1. Field of the Invention
This invention relates to saturable nonwoven materials comprising fluoropolymer fibers and other additional wettable structural organic fibers. Such nonwovens may be used as a liner material for self-lubricating bearing surfaces, as a sealant, in filtration systems, as electrical insulation and in other applications.
2. Description of the Related Art
The use of a woven or knitted fabric as a liner material for self-lubricating bearings is well known in the art. These woven or knitted fabrics typically consist of fluoropolymer yarn and structural yarns (for example, cotton, polyester or glass fiber etc.).
U.S. Pat. Nos. 2,804,886 (White), 3,055,788 (Stanhope et al.), 3,037,893 (White) and GB 861,506 (Wright et al.) disclose the use of woven fluoropolymer fabric in friction applications. However, liners based on such fabrics are very expensive and typically limited to a thickness of about 0.127 mm or greater. Such woven fabrics known in the industry require complex and expensive manufacturing processes and are characterized by a significant resistance to heat flow. This heat resistance results in the bearings becoming overheated at or above relative speeds in the range of about 0.5 m/s causing increased levels of friction, thus reducing their service life, as indicated by a significant loss of liner material, thereby limiting their operating conditions and requiring more numerous replacements of such liners which results in increased production or operating costs.
Also, a nonwoven structure comprising fluoropolymer fibers and an amount of a binder sufficient to provide an appropriate level of wet and dry strength to the nonwoven structure is well known in the art. U.S. Pat. No. 3,114,672 (Schott) discloses such a material, wherein it can be used for the filtration of hot gases that are chemically active.
Also known in the art, is a pressboard material, which consists of m-aramid fiber, m-aramid fibrids, and fluoropolymer fiber. The pressboard material is primarily utilized as electrical insulation as is described in U.S. Pat. No. 4,888,578 (Hendren, Provost et al.).
The present invention offers the advantage of providing a saturable or open porous, nonwoven structure, which can be impregnated with a resin such that the resin permeates throughout the entire structure, comprising fluoropolymer fibers blended with other additional wettable structural organic fibers. Additionally, saturable nonwoven structures having the thickness of the present invention and the applications of the present invention have not been described in the art. Further, the present invention addresses the problems recognized within the industry that are encountered through the use of thick woven fabrics by providing a thin structure. Further, the present invention offers several other advantages in that it can be used at higher speeds than conventional materials, or it can be used at similar speeds as conventional materials yet have an increased service life, and it may be utilized at higher loading capacities.